The present invention relates to a method for the solidification of radioactive ion exchanger resins for permanent, noncontaminating storage, wherein the ion exchanger resin in powdered and/or spherical form is well mixed by stirring with a cement and water and is then left to stand at room temperature for hardening.
In nuclear energy plants, organic ion exchangers or ion exchanger resins, are used to clean coolant waters or to treat aqueous solutions. These ion exchanger resins absorb radioactive contaminants while they are in use until their capacity has been exhausted. Since the radioactive substances in such spent and no longer usable ion exchanger resins are not firmly bound, the resins must be embedded in a leaching resistant matrix and solidified before they are put into permanent storage. It has been known for a long time to mix water which contains ion exchanger resins with cement which then hardens while absorbing water and encases the ion exchanger resins. The products obtained in this way, which consist of cement blocks with incorporated resin, have relatively poor properties. It has been noted, for example, that after a relatively short time of storage, such cement blocks exhibit cracks and may break up, sometimes even into smaller pieces. Light impacts accelerate or augment the release of breaking out of parts of the solidified product. The chemical stability of such products is also relatively slight. Generally such ion exchanger cement block products break up after only a few days if they are stored in water at room temperature. This means that the effective surface area susceptible to leaching is immensely enlarged by this decaying process and retention of the radioactive substances in the solified block is no longer assured in every case.
It has been proposed to permanently avoid such unacceptable changes in the properties of ion exchanger cement blocks by adding to the ion exchanger-water-cement mixture before hardening a substance which has the capability of preventing the penetration of water to the grains of the ion exchanger resin in the solidified block, as disclosed in German Offenlegungsschrift [laid-open application] No. 2,549,195. Substances which have been suggested to be suitable for this purpose include polymer material, such as polyvinyl propionate, or another linear polymer, such as, for example, polyvinyl acetate or polyvinyl butyrate, or an epoxy resin or another polymer having the capability of undergoing cross-linking reactions, such as, for example, a phenol formaldehyde resin, or a silicone; such substances may also be an alkali silicate, such as waterglass, an organic hydrolizable silicate, such as tetraethyl silicate, as well as a monomeric organic ester of higher fatty acids, such as, for example, an ester of palmitic acid or stearic acid with glycol or glycerine.
It has been proposed to add to the still liquid mixture 0.1 to 20 parts by weight, per 100 parts by weight of cement, of a substance which blocks the penetration of water. In this way, it has been disclosed 26 parts by weight dry ion exchanger resin, i.e. not quite 14 percent by weight, can be solidified. However, this method is not only complicated but also very expensive. In the solidification of radioactive substances, as well as in their transport and removal or permanent storage, respectively, the cost factor plays an important part. Improvements of the properties of the solidified product of ion exchange resins, water and cement, such as, for example, sufficient compressive strength of the hardened product (of the order of magnitude of 10 N/mm.sup.2) and thus also long-term stability, high leaching resistance and great capability to absorb ion exchanger resin, i.e. a larger amount of resin in the final product, are in competition with processability and cost factors.